Rationale:
Removal of obsolete feature that has been replaced by noexcept.

Effect on original feature:
A valid C++ 2017 function declaration, member function declaration, function
pointer declaration, or function reference declaration that uses throw()
for its exception specification will be rejected as ill-formed in this
International Standard.

It should simply be replaced with noexcept for no
change of meaning since C++ 2017.

There is no way to write a function declaration
that is non-throwing in this International Standard
and is also non-throwing in C++ 2003
except by using the preprocessor to generate
a different token sequence in each case.